1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device, and more specifically to a method of forming a contact hole for connecting conductive layers insulated by an interlayer insulating film.
2. Description of the Related Art
According to conventional methods, a contact hole is formed in a semiconductor device as follows. First, appropriate impurities are injected into the surface region of the silicon substrate at a desired acceleration voltage and concentration, to form a conductive diffusion layer. Then, silicon oxide film is deposited on the substrate, including the diffusion layer, by a CVD (Chemical Vapor Deposition) method, thereby forming an interlayer insulating film. Thereafter, a desired resist pattern is formed on the interlayer insulating film by photolithography. The interlayer insulating film is etched, using the resist pattern as a mask by an RIE (Reactive Ion Etching) method, forming a contact hole through which the diffusion layer is exposed. After removing the resist pattern, a wiring layer made of polysilicon is formed on the interlayer insulating layer, filling the contact hole. Thus, the wiring layer is electrically connected to the diffusion layer through the contact hole.
In the above-mentioned method, when a contact hole is formed, the exposed area of the diffusion layer is defined by the resist pattern serving as a photomask. Hence, the contact hole cannot be smaller than the opening made in the photomask and, since the photomask cannot have an opening of a diameter less than a certain design rule, it is impossible to form a contact hole smaller than this design rule.